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Radon Levels in Washington County, Iowa

EPA puts Washington County in Zone 1, its highest radon zone, and high results are common there: 54.9% of the 1,186 radon tests reported to CDC (2008 to 2017, laboratory totals) came back at or above 4 pCi/L. Homes with elevated levels occur in all three zones, so only a test measures yours.

Data checked By Radon411Methodology

How to test this homeFind a certified tester

  • Share at 4+ pCi/L

    54.9%

    3.6 pts below IA

    Washington
    54.9%
    Iowa
    58.5%

    1,186 tests, 2008 to 2017

  • Median result

    4.6pCi/L

    Action level reached

    Washington
    4.6 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    1,186

    17th of 99 by tests

    Washington
    1,186
    Polk
    10,945

    Reported to CDC before any fix, 2008 to 2017

  • EPA radon zone

    Zone 1

    Highest potential

    1. Zone 1
    2. 2
    3. 3

    1 highest, 3 lowest

    EPA predicts over 4 pCi/L indoors

  • Rank in Iowa

    73 of 99

    Middle half

    Washington
    54.9%
    Sioux
    84.2%

    By share, of 99 with 30+ tests

Read a result for Washington County

Starts at Washington County's median, 4.6 pCi/L

4.6pCi/L

EPA’s own thresholds; the figures are the area’s, never this home’s.

EPA’s reading of 4.6 pCi/L

At or above 4 pCi/L

  1. Under 20 to 1.9 pCi/L
  2. 2 to 4consider a fix
  3. 4 and aboveEPA says fix it

This result is at or above 4 pCi/L. EPA recommends fixing a home when the radon level is 4 pCi/L or higher. Washington County's median reported result, 2008 to 2017.

Interpret this readingWhat a fix costs

The data

Washington County, At a glance

Washington County at a glance

Predicted: EPA radon zone

EPA Zone 1: highest predicted potential

EPA puts all of Washington County in and predicts an average indoor of greater than 4 pCi/L (greater than 150 Bq/m³) across the county. That is one forecast for the whole county, not a reading of any address in it; homes above EPA's turn up in all three zones.

USGS geologic potential: High across 100% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

Radon tests reported for Washington County, 2008 to 2017, laboratory

Reported results by concentration band, Washington County, 2008 to 2017, laboratory
Under 2 pCi/L: 22%2 to 4 pCi/L: 23%4 pCi/L and above: 55%

Of 1,186 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Washington County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L26422.3%
2 to 4 pCi/L27122.8%
4 pCi/L and above65154.9%
What these figures count

These are the 1,186 tests reported to CDC for Washington County over 2008 to 2017 (laboratory totals), many from homes being sold or already suspected of a problem: they describe the county's reported tests, not this house.

Measured: CDC tracking data. Figure above: 2008 to 2017, laboratory. Measured data period: 2005 to 2017 (every CDC figure on file).

How to read these figures

Washington County, Compared

Washington County radon figures, compared

Calculated by Radon411

More than half: 54.9% of the 1,186 radon tests reported to CDC for Washington County over the 2008 to 2017 laboratory totals read at least 4 pCi/L. That places it 73rd of 99 Iowa counties with 30 or more tests for the same period. That is 3.6 points below the 58.5% pooled from 99 Iowa counties.

The median result, 4.6 pCi/L, sits above EPA's 4 pCi/L action level, and the top reported result was 69.0 pCi/L. The rest split 22.3% under 2 pCi/L and 22.8% from 2 to 4 (Iowa: 21.8% and 19.7%). Zone 1 on EPA's map (predicted average above 4 pCi/L) and a 54.9% share point the same way here.

2 of its 6 bordering counties with figures ran higher, led by Keokuk County at 60.3%; Jefferson County reported 33.5%. Statewide for the same period, Sioux County reported the highest share (84.2%) and Decatur County the lowest (25.9%).

CDC's ten-year totals for Washington County went from 997 tests (2005 to 2014) to 1,186 (2008 to 2017), the share going from 55.4% to 54.9%.

Nationally, every county with a figure for the same period pools to 35.7%; Washington County sits 19.2 points above it. CDC also counts 172 tests taken after mitigation in Washington County for the same period: tests in homes where a fix was already in.

Washington County against Iowa, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Washington County
Washington County1,18654.9%4.6 pCi/LThis county
Iowa, pooled99 counties, pooled95,24558.5%Not pooled+3.6 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled−19.2 points
Sioux Countyhighest in the state1,98284.2%10.7 pCi/L+29.3 points
Decatur Countylowest in the state8525.9%2.5 pCi/L−29.0 points
Keokuk County, IAborders it21460.3%5.2 pCi/L+5.4 points
Iowa County, IAborders it51959.2%5.1 pCi/L+4.3 points
Louisa County, IAborders it9652.1%4.1 pCi/L−2.8 points
Henry County, IAborders it16846.4%3.4 pCi/L−8.5 points
Johnson County, IAborders it7,32141.6%3.2 pCi/L−13.3 points
Jefferson County, IAborders it84133.5%2.6 pCi/L−21.4 points
Where Washington County's reported results fell, 2008 to 2017, laboratory, beside Iowa and the United States
ResultWashington County testsWashington County shareIowa shareU.S. shareAgainst Iowa
Under 2 pCi/L26422.3%21.8%39.6%+0.5 points
2 to 4 pCi/L27122.8%19.7%24.7%+3.1 points
4 pCi/L and above65154.9%58.5%35.7%−3.6 points
Washington County ranked among the 99 Iowa counties with 30 or more tests, by share at or above 4 pCi/L, 2008 to 2017, laboratory
CountyRankTestsAt or above 4 pCi/LMedian
Iowa County68 of 9951959.2%5.1 pCi/L
Chickasaw County69 of 9949859.0%4.9 pCi/L
Cerro Gordo County70 of 991,66259.0%4.8 pCi/L
Dallas County71 of 992,35258.5%4.9 pCi/L
Pottawattamie County72 of 991,86857.4%4.7 pCi/L
Washington County73 of 991,18654.9%4.6 pCi/L
Bremer County74 of 9995753.0%4.3 pCi/L
Jackson County75 of 991,05652.7%4.1 pCi/L
Clinton County76 of 991,37552.7%4.3 pCi/L
Louisa County77 of 999652.1%4.1 pCi/L
Buchanan County78 of 9956451.2%4.1 pCi/L
Washington County ten-year laboratory totals, against Iowa's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestIowa, pooledChange from the row before
2008 to 20171,18654.9%4.6 pCi/L69.0 pCi/L58.5%+0.5 points
2007 to 20161,09554.4%4.5 pCi/L69.0 pCi/L58.6%−0.1 points
2006 to 20151,07154.5%4.6 pCi/L85.4 pCi/L59.4%−0.9 points
2005 to 201499755.4%4.7 pCi/L85.4 pCi/L59.6%First on file

Pooled shares: Radon411's sum of CDC's county counts for one period.

Washington County, Geology

The ground under Washington County

Predicted

USGS's geologic map puts all of Washington County's mapped land in one class: high radon potential. All of it lies in the area the map calls Loess-Covered Drift Plains, to which USGS gives a radon index of 13, in the high band (12 to 17).

USGS's geologic areas under Washington County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Loess-Covered Drift PlainsPre-Illinoian and Illinoian glacial deposits, and loess.High13100%

Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.

Washington County beside the ground around it

On high-potential ground Washington County is close to Iowa as a whole: 100% of its land against 98.8%. Of the 6 counties that border it, none has as large a share of high-potential ground; Henry County comes nearest at 100%.

Share of land by USGS radon potential: Washington County, the 6 counties bordering it and Iowa
AreaEPA zoneLow potentialModerate potentialHigh potential
Washington CountyZone 1NoneNone100%
Jefferson CountyZone 1NoneNone100%
Louisa CountyZone 1NoneNone100%
Henry CountyZone 1NoneNone100%
Keokuk CountyZone 1NoneNone100%
Johnson CountyZone 1NoneNone100%
Iowa CountyZone 1NoneNone100%
Iowa99 counties, pooled by land areaVariesNone1.2%98.8%

The map rates the ground, not the air in any home.

Local help

Washington County, Local resources

Radon testing and mitigation in Washington County

Listed radon businesses with an address in Washington County:

Listed radon professionals by town: Washington, Kalona

What Iowa's program says
Phone
(515) 281-4928
Licensing of radon professionals
Iowa’s radon program approves applications for persons who wish to become certified to perform radon testing or credentialed to perform mitigation and laboratories that provide radon testing devices and analytical services.
Disclosure when a home is sold or rented
However, per Iowa Code chapters 543B.9 and 543B.18 and Iowa Administrative Code 193E Chapter 14 administered by the Iowa Real Estate Commission, a seller must disclose any known tests for the presence of radon and if yes, provide the date of last report and the result(s).

What it means

Washington County, Questions

Questions about radon in Washington County

Are radon levels high in Washington County?

Over the 2008 to 2017 laboratory totals, 54.9% of the radon tests reported to CDC for Washington County, Iowa were at or above 4 pCi/L, and the median reported pre-mitigation result was 4.6 pCi/L. Of 99 Iowa counties with 30 or more tests for the same period, 72 reported a higher share; pooled, the state comes to 58.5%.

Which counties border Washington County?

Washington County borders 6 counties: Jefferson County, Louisa County, Henry County, Keokuk County, Johnson County and Iowa County.

Products

Washington County, Products

Testing a home in Washington County

In Washington County, 54.9% of 1,186 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 58.5% pooled across Iowa. In Zone 1 the year-round level in Washington County is the one to know: a long-term test (more than 90 days) or a monitor, with a short-term kit for a first answer.

Test kits and monitors3

See every kit and monitor

Washington County is in EPA Zone 1, the highest predicted radon potential. Best radon monitors for Zone 1 counties like Washington County

Explore

Washington County, Bordering counties

Counties bordering Washington County

Calculated by Radon411

Washington County, Cities and towns

Cities and towns in Washington County

The Census Bureau estimates 22,667 residents in Washington County for July 1, 2025, 131 more than in 2020 (+0.6%). That works out to 40 people per square mile of land. Its largest town, Washington, has 7,261 residents, 32.0% of the total. Testing is reported here more often than across the state: CDC's 1,186 reported tests for 2008 to 2017 come to 52.3 for every 1,000 residents (2025 estimate), against 29.4 for Iowa.

From Washington to Coppock, CDC publishes no figure by town: each reads Washington County's.

The cities and towns in Washington County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Washington7,261−1.2%32.0%
Kalona2,811+6.4%12.4%
Wellman1,539+1.2%6.8%
Riverside1,086+1.7%4.8%
Keotaextends beyond Washington County888−1.0%Counted whole
Brighton589−1.7%2.6%
Ainsworth512+0.6%2.3%
Crawfordsville278+0.4%1.2%
West Chester147+1.4%0.6%
Coppockextends beyond Washington County35−2.8%Counted whole

10 incorporated places, as listed in the U.S. Census Bureau’s 2020 place reference files. Residents: U.S. Census Bureau population estimates for July 1, 2025 (Vintage 2025). A place that extends beyond Washington County is counted whole, so it has no share.

Washington County, Homes

Homes in Washington County

Washington County is a place of houses on their own lots: 79% of its 9,638 homes are detached single-family houses, against 72% across Iowa. The homes are older than Iowa's as a whole: half were built before 1962 (1971 for Iowa), and 49% date from before 1960. 72% of occupied homes are lived in by their owner (Iowa: 72%); in the rest a tenant can run a test, but a fix is the landlord's to make.

Homes in Washington County, Iowa, 2019 to 2023
HomesWashington CountyIowa
Housing units9,6381,427,175
Detached houses79%72%
In buildings of 5 or more6%14%
Mobile homes4%3%
Built before 196049%39%
Built since 200016%21%
Middle year built19621971
Owner-occupied72%72%

Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.